Sweeping optical scanner of an apparatus for cutting-out a human or animal tissue

ABSTRACT

The present invention relates to an apparatus for cutting-out including a device for treating a L.A.S.E.R. beam generated by a femtosecond laser (1), and positioned downstream from said femtosecond laser, the treatment device comprising:a shaping system (3) positioned on the trajectory of said beam, for modulating the phase of the wave front of the L.A.S.E.R. beam according to a modulation set value calculated for distributing the energy of the L.A.S.E.R. beam in at least two impact points forming a pattern in its focal plane,an optical focusing system (5) downstream from the shaping system, the optical focusing system comprising a concentrator module for focusing the phase-modulated L.A.S.E.R. beam in a focusing plane and a depth-positioning module for displacing the focusing plane into a plurality of cutting-out planes,a sweeping optical scanner (4) positioned between the concentrator module and the depth-positioning module for displacing the pattern in the cutting-out plane in a plurality of positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/091,881, filed on Oct. 5, 2018, now U.S. Pat. No. 11,452,637, whichis a national stage filing under 35 U.S.C. 371 of InternationalApplication No., PCT/CA2020/051447 filed on Oct. 28, 2020, which claimsthe benefit of U.S. Provisional Application No. 62/926,970, filed onOct. 28, 2019. The contents of the aforementioned applications areincorporated by reference in their entirety herein.

TECHNICAL FIELD

The present invention relates to the technical field of surgicaloperations made with a femtosecond laser, and more particularly that ofophthalmological surgery notably for applications for cutting-outcorneas, or lenses.

The invention relates to a device for cutting-out a human or animaltissue, such as a cornea, or a lens, by means of femtosecond laser.

By femtosecond laser, is meant a light source capable of sending aL.A.S.E.R. beam as ultra-short pulses, for which the duration iscomprised between 1 femtosecond and 100 picoseconds, preferablycomprised between 1 and 1,000 femtoseconds, notably of the order ofabout hundred femtoseconds.

PRIOR ART

From the state of the art carrying out surgical operations of the eye isknown by means of a femtosecond laser, such as operations forcutting-out corneas or lenses.

The femtosecond laser is an instrument capable of achieving cutting-outof the corneal tissue for example by focusing a L.A.S.E.R. beam in thestroma of the cornea, and by making a succession of small adjacentcavitation bubbles, which then forms a cutting-out line.

More specifically, during the focusing of the L.A.S.E.R. beam in thecornea, a plasma is generated by non-linear ionization when theintensity of the laser exceeds a threshold value, called an opticalbreakdown threshold. A cavitation bubble is then formed, generating avery localized perturbation of the surrounding tissues. Thus, the volumeactually ablated by the laser is very small comparatively with thedisrupted area.

The area cut out by the laser at each pulse is very small, of the orderof one micron or of tens of microns depending on the power and thefocusing of the beam. Thus, a corneal lamellar cut out may only beobtained by performing a series of contiguous impacts over the wholesurface of the area to be cut out.

The displacement of the beam may then be carried out with a sweepingdevice, consisting of controllable galvanometric mirrors, and/or platesallowing the displacement of optical elements, such as mirrors orlenses. This sweeping device gives the possibility of displacing thebeam along a reciprocal trajectory along a succession of segmentsforming a displacement path of the beam.

In order to cut out a cornea over a surface of 1 mm², about 20,000impacts very close to each other have to be achieved. Today, theseimpacts are made one by one at an average rate of 300,000impacts/second. In order to cut out a cornea over a surface of about 65mm², by taking into account the times during which the laser stops theproduction of the pulses at the end of a segment in order to allow themirrors to be positioned on the next segment, 15 seconds on average arerequired. The surgical cutting-out operation is therefore slow.

In order to optimize the cutting-out time, it is known how to increasethe frequency of the laser. However, increasing the frequency alsoinvolves an increase in the displacement speed of the beam, by means ofsuitable plates or scanners. It is also known how to increase thespacing between the impacts of the laser on the tissue to be cut out,but generally to the detriment of the cutting-out quality.

Most femtosecond lasers for corneal cut out thus use high workingfrequencies, generally greater than 100 kHz, associated with systems fordisplacing the beam combining scanners and displacement plates, whichare a burden to the total cost of the facility, and therefore of theinvoiced surgical operation.

In order to remedy this rapidity problem of the L.A.S.E.R. cutting-out,it is also known how to use galvanometric mirrors for increasing therate, the speed, and the deflection trajectory of the L.A.S.E.R. beam.

However, this technique does not give entire satisfaction in terms ofresults.

Another solution for reducing the cutting-out time consists ofgenerating several cavitation bubbles simultaneously.

Documents US 2010/133246, EP 1790 383 and US 2016/067095 describecutting-out devices based on the subdivision technique of a singleprimary L.A.S.E.R. beam into a plurality of secondary L.A.S.E.R. beams.These devices generally comprise an optical system—such as one (or more)beam separator—to produce secondary L.A.S.E.R. beams for generating arespective cavitation bubble each.

The fact of simultaneously generating “n” cavitation bubbles gives thepossibility of reducing the total duration for cutting-out a factor “n”.

The leverage of a beam into several beams, with the purpose ofaccelerating the procedure, has already been described but always bymeans of purely optical solutions, either by diffraction or by multiplereflections. The result has never been utilized in a clinic, mainlysince the different beams were not of a homogeneous size.

Also, the subdivision technique causes an increase in the diameter ofthe plurality of secondary L.A.S.E.R. beams relative to the diameter ofthe single primary beam L.A.S.E.R. produced by the femtosecond laser. Infact, the secondary L.A.S.E.R. beams correspond to spatially separated“portions” of the single primary L.A.S.E.R. beam. Because of thenon-zero distance between the different secondary L.A.S.E.R. beams, thediameter of the assembly formed by the plurality of secondary L.A.S.E.R.beams is greater than the diameter of the primary L.A.S.E.R. beam.

This increase in diameter can be a drawback, especially in the eventwhere the cutting-out device comprises a sweeping system—such as anoptical scanner—for displacing the plurality of secondary L.A.S.E.R.beams in a cutting-out plane. In fact, the input diameter of a sweepingsystem is generally of the order of the diameter of the single primaryL.A.S.E.R. beam such that some secondary beams do not penetrate thesweeping system.

An object of the present invention is to propose a cutting-out apparatusfor eliminating at least one of the abovementioned drawbacks. Inparticular, an object of the present invention is to propose acutting-out apparatus giving the possibility of producing a cutting-outplane more rapidly than with existing systems and for which the qualityof the cut out is improved.

DISCUSSION OF THE INVENTION

For this purpose, the invention proposes an apparatus for cutting-out ahuman or animal tissue, such as a cornea or a lens, said apparatusincluding a femtosecond laser capable of sending a L.A.S.E.R. beam inthe form of pulses and a device for treating a L.A.S.E.R. beam generatedby the femtosecond laser, the treatment device being positioneddownstream from said femtosecond laser, remarkable in that the treatmentdevice comprises: a shaping system positioned on the trajectory of saidbeam, for modulating the phase of the wave front of the L.A.S.E.R. beamso as to obtain a phase-modulated L.A.S.E.R. single-beam according to amodulation set value calculated for distributing the energy of theL.A.S.E.R. beam in at least two impact points forming a pattern in itsfocal plane, an optical focusing system downstream from the shapingsystem, the optical focusing system comprising a concentrator module forfocusing the phase-modulated L.A.S.E.R. beam in a focusing plane and adepth-positioning module for displacing the focusing plane into aplurality of cutting-out planes, a sweeping optical scanner positionedbetween the concentrator module and the depth-positioning module fordisplacing the pattern in the cutting-out plane in a plurality ofpositions.

Within the scope of the present invention, by “impact point” is meant anarea of the L.A.S.E.R. beam, comprised in its focal plane wherein theintensity of said L.A.S.E.R. beam is sufficient for generating acavitation bubble in a tissue.

Within the scope of the present invention, by “adjacent impact points”,are meant two impact points positioned facing each other and notseparated by another impact point. By “neighboring impact points” aremeant two points of a group of adjacent points between which thedistance is a minimum.

Within the scope of the present invention, by “pattern” is meant aplurality of L.A.S.E.R. impact points simultaneously generated in afocusing plane of a shaped L.A.S.E.R. beam—i.e. phase modulated fordistributing its energy in several distinct spots in the focusing planecorresponding to the cutout plane of the device.

Thus, the invention gives the possibility of modifying the intensityprofile of the L.A.S.E.R. beam in the cutout plane, so as to be able toimprove the quality or else the speed of the cutting-out depending onthe selected profile. This intensity profile modification is obtained byphase modulation of the L.A.S.E.R. beam.

The optical phase modulation is achieved by means of a phase mask. Theenergy of the incident L.A.S.E.R. beam is preserved after modulation,and the shaping of the beam is achieved by acting on its wave front. Thephase of an electromagnetic wave represents the instantaneous situationof the amplitude of an electromagnetic wave. The phase depends both onthe time and on the space. In the case of the spatial shaping of aL.A.S.E.R. beam, only the variation in the phase space are considered.

The wave front is defined as the surface of the points of a beam havingan equivalent phase (i.e. the surface consisting of the points for whichthe travel times from the source having emitted the beam are equal). Themodification of the spatial phase of a beam therefore requiresmodification of its wave front.

This technique gives the possibility of achieving the cutting-outoperation in a more rapid and more efficient way since it appliesseveral L.A.S.E.R. spots each achieving a cut out and according to acontrolled profile.

In terms of the present invention, the phase modulation of the wavefront generates a modulated single L.A.S.E.R. beam which forms severalimpact points only in the cutout plane. In this way, the modulatedL.A.S.E.R. beam is single all the way along the propagation path. Thephase modulation of the wave front delays or advances the phase of thedifferent points of the surface of the beam relative to the initial wavefront so that each of these points produces constructive interference atN separate points in the focal plane of a lens. This redistribution ofenergy into a plurality of impact points occurs in a single plane only(i.e. the focusing plane) and not all the way along the propagation pathof the modulated L.A.S.E.R. beam.

By contrast, document US 2010/0133246 proposes using an optical systembased on phase and allowing a primary beam to be subdivided into aplurality of secondary beams having different angles of propagation.

The modulation technique according to the invention (by generation of amodulated unique L.A.S.E.R. beam) limits the risks of degradation of thequality of the cut-out surface. In fact, if a portion of the solemodulated L.A.S.E.R. beam is lost along the propagation path of thebeam, the intensities of all the impact points of the pattern will beattenuated at the same time (conservation of uniformity between thedifferent impact points of the pattern) but no impact point willdisappear in the cutout plane. By contrast with the technique of beamsubdivision proposed in US 2010/0133246, if a portion of the pluralityof secondary beams is lost along the propagation path, some impactpoints of the pattern (corresponding to the impact points generated bythe lost secondary beams) will be missing from the cutout plane, whichsubstantially degrades the quality of the cut-out performed.

Preferred but non-limiting aspects of the cutting-out apparatus are thefollowing:

-   -   the apparatus may further comprise a control unit of the optical        scanner for controlling the displacement of the pattern along a        displacement path comprising at least one segment in the        cutting-out plane;    -   the control unit can be programmed for controlling the        activation of the femtosecond laser such that the distance        between two adjacent positions of the pattern along a segment of        the displacement path being greater than or equal to the        diameter of an impact point of the pattern;    -   the control unit can be adapted for controlling the displacement        of the pattern along a displacement path comprising a plurality        of segments, the distance between two adjacent segments of the        displacement path being greater than the dimension of the        pattern along a perpendicular to the displacement direction of        the pattern;    -   the control unit can be programmed for controlling the        displacement of the pattern along a displacement path comprising        a plurality of parallel segments, the distance between two        neighboring segments of the displacement path being constant and        less than or equal to 3N times the diameter of an impact point,        where N corresponds to the number of impact points of the        pattern;    -   the control unit can be programmed for controlling the        displacement of the pattern along a displacement path comprising        a plurality of parallel segments, the distance between at least        two neighboring segments being different from the distance        between at least two other neighboring segments;    -   the control unit may be able to control the displacement of the        pattern along a notch-shaped displacement path in the        cutting-out plane;    -   the control unit may be able to control the displacement of the        pattern along a spiral-shaped displacement path in the        cutting-out plane;    -   the sweeping optical scanner may include at least one optical        mirror pivoting around at least two axes, the control unit of        the optical scanner controlling the pivoting of the mirror so as        to displace the pattern along the displacement path;    -   the apparatus may further comprise at least one Dove prism        positioned between the shaping system and the sweeping optical        scanner;    -   the control unit may further be programmed for controlling the        activation of the femtosecond laser, the control unit activating        the femtosecond laser when the sweeping rate of the optical        scanner is greater than a threshold value.    -   the apparatus can also comprise a filter arranged downstream of        the shaping system to block parasite energy generated at the        center of the shaping system;    -   the filter can comprise a plate including: a zone opaque to        L.A.S.E.R. radiation arranged at the center of the plate, and a        zone transparent to L.A.S.E.R. radiation extending to the        periphery of the opaque zone.    -   the shaping system can consist of a set of phase masks, each        mask acting on the phase of the L.A.S.E.R. beam to distribute        the energy of the L.A.S.E.R. beam by phase modulation according        to a distinct pattern, the masks being fixed to a displacement        device, the control unit being programmed for controlling the        displacement device (via emission of one or more control        signals) so as to shift each mask between:        -   an active position in which the mask cuts the optical path            of the L.A.S.E.R. beam, and        -   an inactive position in which the mask does not extend over            the optical path of the L.A.S.E.R. beam;    -   the shaping system can consist of a spatial light modulator, the        control unit being programmed for controlling the spatial light        modulator by emission of at least one control signal, each        control signal causing display on the spatial light modulator of        a phase mask forming a modulation set value;    -   the control unit can be programmed for controlling the shaping        system, said control unit being adapted to send at least first        and second control signals (between two respective cutout planes        or in the same cutout plane):        -   the first control signal causing modulation of the phase of            the wave front of the L.A.S.E.R. beam according to a first            modulation set value calculated to distribute the energy of            the L.A.S.E.R. beam into a plurality of first impact points            in the focal plane of the shaping system, the first impact            points constituting a first pattern,        -   the second control signal causing modulation of the phase of            the wave front of the L.A.S.E.R. beam according to a second            modulation set value calculated to distribute the energy of            the L.A.S.E.R. beam into a plurality of second impact points            in the focal plane of the shaping system, the second impact            points constituting a second pattern different to the first            pattern.

The invention also relates to a control process of apparatus for cuttingout human or animal tissue, such as a cornea, or a crystalline, theapparatus including a femtosecond laser capable of sending a L.A.S.E.R.beam in the form of pulses, and a treatment device arranged downstreamof the femtosecond laser for processing the L.A.S.E.R. beam generated bythe femtosecond laser, the treatment device comprising:

-   -   Shaping the L.A.S.E.R. beam to modulate the phase of the wave        front of the L.A.S.E.R. beam so as to obtain a single        phase-modulated L.A.S.E.R. beam according to a modulation set        value calculated to distribute the energy of the L.A.S.E.R. beam        in at least two impact points forming the pattern in its focal        plane,    -   Focusing the modulated L.A.S.E.R. beam to focus the        phase-modulated L.A.S.E.R. beam in a focal plane,    -   Displacement of the pattern in the cutout plane into a plurality        of positions.

Preferred, but non-limiting, aspects of the cutting-out apparatus arethe following:

-   -   the displacement step can consist of displacing the pattern        along a displacement path comprising at least a segment in the        cutout plane,    -   the process can also comprise an activation step of the        femtosecond laser such that the distance between two adjacent        positions of the pattern along a segment of the displacement        path is greater than or equal to an impact point of the pattern,    -   the displacement step can consist of displacing the pattern        along a displacement path comprising a plurality of segments,        the distance between two adjacent segments of the displacement        path being greater than the dimension of the pattern according        to a perpendicular to the displacement direction of the pattern,    -   the displacement step can consist of displacing the pattern        along a displacement path comprising a plurality of parallel        segments, the distance between two adjacent segments of the        displacement path being constant and less than or equal to 3N        times the diameter of an impact point, where N corresponds to        the number of impact points of the pattern,    -   the displacement step can consist of displacing the pattern        along a displacement path comprising a plurality of parallel        segments, the distance between at least two adjacent segments        being different to the distance between at least two other        adjacent segments,    -   the displacement step can consist of displacing the pattern        according to a displacement path in the form of a slot in the        cutout plane,    -   the displacement step can consist of displacing the pattern        according to a displacement path in the form of a spiral in the        cutout plane,    -   the process can also comprise an activation step of the        femtosecond laser, the control unit activating the femtosecond        laser when the scanning speed of the optical scanner is greater        than a threshold value,    -   the process can also comprise a filtering step of the L.A.S.E.R.        beam to block parasite energy generated at the center of a        shaping system,    -   the modulated shaping step can comprise the sub-steps consisting        of: modulating the phase of the wave front of the L.A.S.E.R.        beam according to a first modulation set value calculated to        distribute the energy of the L.A.S.E.R. beam into a plurality of        first impact points in the focal plane of the shaping system,        the first impact points constituting a first pattern, and to        modulate the phase of the wave front of the L.A.S.E.R. beam        according to a second modulation set value calculated to        distribute the energy of the L.A.S.E.R. beam into a plurality of        second impact points in the focal plane of the shaping system,        the second impact points constituting a second pattern different        to the first pattern,    -   the modulation set value can be a phase mask calculated by using        an iterative algorithm based on the Fourier transform.

SHORT DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become clearlyapparent from the description which is made hereafter thereof, as anindication and by no means as a limitation, with reference to theappended figures, wherein:

FIG. 1 is a schematic illustration of a circuit including thecutting-out apparatus according to the invention;

FIG. 2 illustrates an intensity distribution of a L.A.S.E.R. beam in itsfocal plane;

FIG. 3 illustrates a displacement path of a cut out pattern;

FIG. 4 illustrates planes for cutting-out a volume of tissue to bedestroyed;

FIGS. 5 to 9, 11A, 11B, 11C, 12 to 18, and 20 to 22, 24 and 28illustrate different examples of a cut out pattern,

FIGS. 10, 19, 23 and 25 to 27 illustrate matrices of cavitation bubbles.

DETAILED DISCUSSION OF THE INVENTION

The invention relates to an apparatus for cutting-out a human tissue bymeans of a femtosecond laser. In the subsequent description, theinvention will be described, as an example, for cutting-out a cornea ofa human or animal eye.

1. CUTTING-OUT APPARATUS

With reference to FIG. 1 , an embodiment of the cutting-out apparatusaccording to the invention is illustrated. The latter may be positionedbetween a femtosecond laser 1 and a target to be treated 2.

The femtosecond laser 1 is able to emit a L.A.S.E.R. beam as pulses. Asan example, the laser 1 emits a light with a wavelength of 1,030 nm inthe form of pulses of 400 femtoseconds. The laser 1 has a power of 20 Wand a frequency of 500 kHz.

The target 2 is for example a human or animal tissue to be cut out suchas a cornea or a lens.

The cutting-out apparatus comprises:

-   -   a shaping system 3 positioned on the trajectory of the        L.A.S.E.R. beam 11 stemming from the femtosecond laser 1,    -   a sweeping optical scanner 4 downstream from the shaping system        3,    -   an optical focusing system 5 downstream from the sweeping        optical scanner 4.

The cutting-out apparatus also comprises a control unit 6 allowingcontrol of the shaping system 3, the sweeping optical scanner 4 and theoptical focusing system 5.

The shaping system 3 allows modulation of the phase of the L.A.S.E.R.beam 11 stemming from the femtosecond laser 1 in order to distribute theenergy of the L.A.S.E.R. beam in a plurality of impact points in itsfocal plane, this plurality of simultaneously generated impact pointsdefining a pattern.

The sweeping optical scanner 4 gives the possibility of orienting thephase-modulated L.A.S.E.R. beam 31 stemming from the shaping system 3for displacing the cut out pattern along a displacement path predefinedby the user in the focusing plane 21.

The optical focusing system 5 allows displacement of the focusing plane21—corresponding to the cutout plane—of the modulated and deviatedL.A.S.E.R. beam 41.

Thus, the shaping system 3 allows simultaneous generation of severalimpact points defining a pattern, the sweeping optical scanner 4 allowsdisplacement of this pattern in the focusing plane 21, and the opticalfocusing system 5 allows displacement of the focusing plane 21 in depthso as to generate cut outs in successive planes defining a volume.

The different elements forming the cutting-out apparatus will now bedescribed in more details with reference to the figures.

2. ELEMENTS OF THE CUTTING-OUT APPARATUS

2.1. Shaping System

The spatial shaping system 3 of the L.A.S.E.R. beam gives thepossibility of varying the wave surface of the L.A.S.E.R. beam in orderto obtain impact points separated from each other in the focal plane.More specifically, the shaping system 3 allows modulation of the phaseof the L.A.S.E.R. beam 11 stemming from the femtosecond laser 1 so as toobtain a phase-modulated L.A.S.E.R. single-beam according to amodulation set value calculated to form intensity peaks in the focalplane of the beam, each intensity peak producing a respective impactpoint in the focal plane corresponding to the cutout plane.

The fact of having a modulated L.A.S.E.R. single-beam makes for easyintegration of a sweeping system—such as an optical scanner—fordisplacing the plurality of secondary L.A.S.E.R. beams in a cutoutplane. In fact, since the input diameter of a sweeping system is of theorder of the diameter of the initial L.A.S.E.R. beam, the use of amodulated L.A.S.E.R. single-beam (the diameter of which is substantiallyequal to the diameter of the initial L.A.S.E.R. beam) limits the risksof aberration which can occur with the technique of beam subdivisionsuch as described in US 2010/0133246.

The shaping system 3 is, according to the illustrated embodiment, aspatial light modulator with liquid crystals, known under the acronym ofSLM, for “Spatial Light Modulator”. The inventors actually found thatusing an SLM was advantageous despite the basic ideas of the prior artwhich dissuade the skilled person from using such a device (seeespecially paragraph [0024] of document US 2015/0164689).

The SLM allows modulation of the final distribution of energy of theL.A.S.E.R. beam, notably in the focal plane 21 corresponding to thecutout plane of the tissue 2. More specifically, the SLM is adapted formodifying the spatial profile of the wave front of the primaryL.A.S.E.R. beam 11 stemming from the femtosecond laser 1 fordistributing the energy of the L.A.S.E.R. beam in different focusingpoints in the focusing plane.

This device limits costs associated with modulation of the phase of thewave front and resolves the problems linked to industrialization of theproposed solution. The phase modulation of the wave front may beconsidered as a two-dimensional interference phenomenon. Each portion ofthe initial L.A.S.E.R. beam stemming from the source is retarded oradvanced relatively to the initial wave front so that each of theseportions are redirected so as to produce constructive interference in Ndistinct points in the focal plane of a lens. This energy redistributionin a plurality of impact points only occurs in a single plane (i.e. thefocusing plane) and not at all along the propagation path of themodulated L.A.S.E.R. beam. Thus, the observation of the modulatedL.A.S.E.R. beam before or after the focusing plane does not give thepossibility of identifying a redistribution of the energy in a pluralityof distinct impact points, because of this phenomenon which may beassimilated to constructive interferences (which only take place in aplane and not at all along the propagation like in the case of theseparation of an initial L.A.S.E.R. beam in a plurality of secondaryL.A.S.E.R. beams).

In order to better understand this phase modulation phenomenon of thewave front, intensity profiles 32 a-32 e obtained for three examples ofdistinct optical circuits have been schematically illustrated in FIG. 2. As illustrated in FIG. 2 , a L.A.S.E.R. beam 11 emitted by a lasersource 1 produces an intensity peak 32 a with a Gaussian shape in animpact point 33 a in a focusing plane 21. The insertion of a beamsplitter 7 between the source 1 and the focusing plane 21 induces thegeneration of a plurality of secondary L.A.S.E.R. beams 71, eachsecondary L.A.S.E.R. beam 71 producing a respective impact point 33 b,33 c in the focusing plane 21 of the secondary L.A.S.E.R. beams 71.Finally, the insertion between the source 1 and the focusing plane 21 ofan SLM 3 programmed by means of a phase mask forming a modulation setvalue induces modulation of the phase of the wave front of theL.A.S.E.R. beam 11 stemming from the source 1. The L.A.S.E.R. beam 31for which the phase of the wave front has been modulated gives thepossibility of inducing production of several intensity peaks 33 d, 33 espatially separated in the focal plane 21 of the L.A.S.E.R. beam, eachpeak 32 d, 32 e corresponding to a respective impact point 33 d, 33 eproducing a cut out. The modulation technique of the phase of the wavefront gives the possibility of generating several simultaneouscavitation bubbles without any multiplication of the initial L.A.S.E.R.beam produced by the femtosecond laser 1.

The SLM is a device consisting of a layer of liquid crystals withcontrolled orientation giving the possibility of shaping dynamically thewave front, and therefore the phase of the L.A.S.E.R. beam. The layer ofliquid crystals of an SLM is organized like a grid (or matrix) ofpixels. The optical thickness of each pixel is electrically controlledby orienting the liquid crystal molecules belonging to the surfacecorresponding to the pixel. The SLM (9) makes use of the anisotropyprinciple of liquid crystals, i.e. the modification of the index of theliquid crystals, depending on their spatial orientation. The orientationof liquid crystals may be achieved by means of an electric field. Thus,the modification of the index of the liquid crystals modifies the wavefront of the L.A.S.E.R. beam (4).

In a known way, the SLM applies a phase mask, i.e. a map determining howthe phase of the beam has to be modified for obtaining a given amplitudedistribution in its focusing plane. The phase mask is a two-dimensionalimage, each point of which is associated with a respective pixel of theSLM. This phase mask gives the possibility of controlling the index ofeach liquid crystal of the SLM by converting the value associated witheach point of the mask—illustrated in gray levels comprised between 0and 255 (therefore from black to white)—into a control value—representedin a phase comprised between 0 and 2π. Thus, the phase mask is amodulation set value displayed on the SLM for causing by reflection anuneven spatial phase shift of the L.A.S.E.R. beam (4) illuminating theSLM. Of course, one skilled in the art will appreciate that the graylevel range may vary depending on the SLM version used. For example incertain cases, the gray level range may be comprised between 0 and 220.The phase mask is generally calculated by

-   -   an iterative algorithm based on the Fourier transform, such as        an algorithm of “IFTA” type, acronym for “Iterative Fourrier        Transform Algorithm”, or by    -   diverse optimization algorithms, such as genetic algorithms, or        simulated annealing.

This allows controlling the homogeneity, the intensity, the quality andthe form of the different impact points generated in the cutout plane.

Different phase masks may be applied to the SLM depending on the numberand on the position of the impact points desired in the focal plane ofthe L.A.S.E.R. beam. In every case, one skilled in the art knows how tocalculate a value in each point of the phase mask in order to distributethe energy of the L.A.S.E.R. beam in different focusing spots in thefocal plane.

The SLM therefore gives the possibility, from a Gaussian L.A.S.E.R. beamgenerating a single impact point, and by means of the phase mask, ofdistributing its energy by phase modulation so as to simultaneouslygenerate several impact points in its focusing plane from a singleL.A.S.E.R. beam shaped by phase modulation (a single beam upstream anddownstream from the SLM).

In addition to a reduction in the time for cutting-out the cornea, thephase modulation technique of the L.A.S.E.R. beam according to theinvention allows other improvements, such as a better surface qualityafter cutting-out or reducing the endothelial mortality. The differentimpact points of the pattern may for example be regularly spaced outover the two dimensions of the focal plane of the L.A.S.E.R. beam, so asto form a grid of L.A.S.E.R. spots.

Thus, the shaping system 3 gives the possibility of carrying out asurgical cutting-out operation in a rapid and efficient way. The SLMgives the possibility of shaping dynamically the wave front of theL.A.S.E.R. beam, since it may be parameterized digitally. Thismodulation allows shaping of the L.A.S.E.R. beam in a dynamic andreconfigurable way.

The SLM may be configured for shaping the wave front of the L.A.S.E.R.beam in any other way. For example, each impact point may have anygeometrical shape, other than circular (for example an ellipse, etc.).This may have certain advantages depending on the consideredapplication, such as an increase in the speed and/or the quality of thecut out.

2.2. Sweeping Optical Scanner

The sweeping optical scanner 4 allows deviation of the phase modulatedL.A.S.E.R. beam 31 so as to displace the pattern 8 in a plurality ofpositions 43 a-43 c in the focusing plane 21 corresponding to the cutoutplane.

The sweeping optical scanner 4 comprises:

-   -   an input orifice for receiving the phase-modulated L.A.S.E.R.        beam 31 stemming from the shaping unit 3,    -   one (or several) optical mirror(s) pivoting around at least two        axes for deviating the phase-modulated L.A.S.E.R. beam 31, and    -   an output orifice for sending the deviated modulated L.A.S.E.R.        beam 41 towards the optical focusing system 5.

The optical scanner 4 used is for example a sweeping head IntelliScanIII from SCANLAB AG.

The input and output orifices of such an optical scanner 4 have adiameter of the order of 10 to 20 millimeters, and the sweeping rateswhich may be attained are of the order of 1 m/s to 10 m/s.

The mirror(s) is (are) connected to motor(s) in order to allow theirpivoting. These motor(s) for the pivoting of the mirror(s) is (are)advantageously controlled by the unit of the control unit 6 which willbe described in more details subsequently.

The control unit 6 is programmed for controlling the sweeping opticalscanner 4 so as to displace the pattern 8 along a displacement path 42contained in the focusing plane 21. In certain embodiments, thedisplacement path 42 comprises a plurality of cutting-out segments 42a-42 c. The displacement path 42 may advantageously have a niche shape.In this case, if the optical scanner 4 begins with a first cutting-outsegment 42 a on the left, it will begin with the second cutting-outsegment 42 b on the right, and then the third cutting-out segment 42 con the left, and then the next segment on the right, and so forth overthe whole displacement path 42 of the pattern 8. This will give thepossibility of accelerating the cutting-out of the tissue while avoidingthe requirement for the optical scanner 4 of repositioning the pattern 8at the beginning of each successive cutting-out segment 42 a-42 c.

In order to further accelerate the cutting-out operation in the focusingplane 21, the displacement path 42 may advantageously have a spiralshape. This gives the possibility of maintaining constant the sweepingrate of the optical scanner 4 in the whole cutout plane. Indeed, in thecase of a displacement path 42 with the shape of a niche, the opticalscanner 4 has to stop at the end of each cutting-out segment 42 a formoving on to the next cutting-out segment 42 b, which consumes time.

The sweeping of the beam has an influence on the result of the obtainedcut out. Indeed, the sweeping rate used, as well as the pitch of thesweeping are parameters which influence the quality of the cut out.

Preferably, the sweeping pitch—corresponding to the distance “dist”between two adjacent positions 43 a, 43 b of the pattern 8 along asegment of the displacement path 42—is selected to be greater than orequal to the diameter of an impact point 81 of the pattern 8. This givesthe possibility of limiting the risks of superposing impact pointsduring successive shots.

Also, when the displacement path 42 has a niche shape, the distance “ec”between two adjacent segments 42 a, 42 b of the displacement path 42 ispreferably selected to be greater than the size of the pattern 8 along aperpendicular to its displacement direction. This also gives thepossibility of limiting the risk of superposition of the impact points81 during successive shots.

Finally, for limiting the duration of the cutting-out operation in thecutting-out plane, while guaranteeing a certain quality of thecutting-out, the distance between two adjacent segment 42 a, 42 b of thedisplacement path 42 may be selected to be equal to a maximum (andpreferably less than) of 3N times the diameter of an impact point 81,wherein N is the number of impact points of the pattern 8.

In an embodiment, the cutting-out apparatus further comprises a Doveprism. The latter is advantageously positioned between the shapingsystem 3 and the sweeping optical scanner 4. The Dove prism gives thepossibility of applying a rotation of the pattern 8 which may be usefulin certain applications or for limiting the size of the area forinitiating each cut-out segment 42 a-42 c.

Advantageously, the control unit 6 may be programmed for activating thefemtosecond laser 1 when the sweeping rate of the optical scanner 4 isgreater than a threshold value.

This gives the possibility of synchronizing the emission of theL.A.S.E.R. beam 11 with the sweeping of the sweeping optical scanner 4.More specifically, the control unit 6 activates the femtosecond laser 1when the pivoting rate of the mirror(s) of the optical scanner 4 isconstant. This gives the possibility of improving the quality of thecutting-out for producing a homogenous surfacing of the cutting-outplane.

2.3 Optical Focusing System

The optical focusing system 5 gives the possibility of displacing thefocusing plane 21 of the modulated and deviated L.A.S.E.R. beam 41 in aplane for cutting-out the tissue 2, desired by the user.

The optical focusing system 5 comprises:

-   -   an input orifice for receiving the phase-modulated and deviated        L.A.S.E.R. beam from the sweeping optical scanner,    -   one (or several) motor-driven lens(es) for allowing its (their)        displacement in translation along the optical path of the        phase-modulated and deviated L.A.S.E.R. beam, and    -   an output orifice for sending the focused L.A.S.E.R. beam        towards the tissue to be treated.

The lens(es) used with the optical focusing system 5 may be f-thetalenses or telecentric lenses. With f-theta and telecentric lenses, it ispossible to obtain a focusing plane over the whole field XY, unlikestandard lenses for which it is curved. This gives the possibility ofguaranteeing a constant focused beam size over the whole field. Forf-theta lenses, the position of the beam is directly proportional to theangle applied by the scanner while the beam is always normal to thesample for telecentric lenses.

The control unit 6 is programmed for controlling the displacement of thelens(es) of the optical focusing system 5 along an optical path of theL.A.S.E.R. beam so as to displace the focusing plane 21 in at leastthree respective cutting-out planes 22 a-22 e so as to form a stack ofcutting-out planes of the tissue 2. This gives the possibility ofperforming a cut-out in a volume 23, for example within the scope ofrefractive surgery.

The control unit 6 is able to control the displacement of the opticalfocusing system 5 in order to displace the focusing plane 21 between afirst extreme position 22 a and a second extreme position 22 e, in thisorder. Advantageously, the second extreme position 22 e is closer to thefemtosecond laser 1 than the first extreme position 22 a.

Thus, the cutting-out planes 22 a-22 e are formed by beginning with thedeepest cutout plane 22 a in the tissue and by stacking the successivecutout planes up to the most superficial cutout plane 22 e in the tissue2. Problems associated with the penetration of the L.A.S.E.R. beam intothe tissue 2 are thereby avoided. Indeed, the cavitation bubbles form anopaque barrier of bubbles (known under the name of “OBL”, an acronym for“Opaque Bubble Layer”) preventing propagation of the energy from theL.A.S.E.R. beam under the latter. It is therefore preferable to begin bygenerating the deepest cavitation bubbles in priority in order toimprove the efficiency of the cutting-out apparatus.

Preferably, the length of the optical path between the shaping system 3and the optical focusing system 5 is less than 2 meters, and even morepreferentially less than 1 meter. This gives the possibility of limitingthe power losses due to the energy dispersed over the optical path.Indeed, the larger the distance between the shaping system 3 and theoptical focusing system 5, the larger is the power loss over the path.

Advantageously, the control unit 6 may be programmed for varying theshape of the pattern 8 between two successive cutout planes 22 a-22 b(or 22 b-22 c, or 22 c-22 d, or 22 d-22 e). Indeed, during thecutting-out in a volume 23, it may be preferable to increase theaccuracy of the cutting-out in the peripheral cutout planes 22 a, 22 eand to increase the cutting-out rate in the intermediate cutout planes22 b, 22 c, 22 d located between the peripheral cutout planes 22 a, 22e. For example, in the case of the cutting-out of a volume 23 consistingof a stack of five cutout planes 22 a-22 e, the control unit 6 maycontrol the shaping system 3 by transmitting to it:

-   -   a first phase mask corresponding to a first pattern allowing an        increase in the accuracy of the cutting-out when the focusing        plane corresponds to the first and second cutout planes 22 a and        22 e,    -   a second phase mask when the focusing plane corresponds to the        second, third and fourth cutout planes 22 b-22 d.

Also, the control unit 6 may be programmed for varying the pitch “dist”of the sweeping optical scanner 4 and/or the shape of the cut-out area(by modifying the displacement path of the pattern) between tworespective cutout planes. This also gives the possibility either ofincreasing the accuracy of the cutting-out, or the cutting-out rate inone cutout plane to another.

Finally, the control unit 6 may be programmed for controlling thesweeping optical scanner 4 so as to vary the area cut out in thefocusing plane 21 between two successive cutout planes 22 d, 22 e. Thisgives the possibility of varying the shape of the finally cut-out volume23 depending on the targeted application.

Preferably, the distance between two successive cutout planes iscomprised between 2 μm and 500 μm, and notably:

-   -   between 2 and 20 μm for treating a volume requiring great        accuracy, for example in refractive surgery, with preferably a        spacing comprised between 5 and 10 μm, or    -   between 20 and 500 μm for treating a volume not requiring great        accuracy, such as for example for destroying the central portion        of a lens core, with preferably a spacing comprised between 50        and 200 μm.

Of course, this distance may vary in a volume 23 consisting of a stackof cutout planes 22 a-22 e.

2.4 Filter

The cutting-out apparatus can also comprise a filter arranged downstreamof the shaping system 3.

On the one hand the filter blocks the “parasite” energy generated at thecenter of the shaping system 3 (phenomenon known as “zero order”). Infact, during the phase modulation of the L.A.S.E.R. beam with theshaping system, part of the L.A.S.E.R. beam originating from the lasersource 1 is not modulated (because of the space existing between thepixels of the liquid crystals of the SLM). This part of thenon-modulated L.A.S.E.R. beam can cause generation of an energy peakforming at the center of the SLM.

The filter also limits the risk of L.A.S.E.R. lesions unexpected for thepatient in the event of malfunction of the shaping system 3. In fact, ifthe shaping system 3 is defective, the L.A.S.E.R. beam is not modulated,which causes formation of a high-energy peak at the center of theshaping system 3. By blocking this high-energy peak, the filter preventsunintentional generation of cavitation bubbles.

The filter can be placed between two converging lenses arrangeddownstream of the shaping system 3. In fact, the order 0 can beeliminated in a Fourier plane only (that is, in the focal point of alens), where shaping of the beam takes place.

The filter consists for example of a plate transparent to L.A.S.E.R.radiation over its entire surface with the exception of a central regionof the plate which is opaque to L.A.S.E.R. radiation. To make thecentral region of the plate opaque to L.A.S.E.R. radiation, the filtercan comprise an opaque lozenge arranged at the center of the surface,the lozenge having a diameter greater than or equal to the diameter of aL.A.S.E.R. beam.

This filter is then positioned such that a straight line normal to theshaping system 3, and passing through the center of said shaping system3 also passes through the central region opaque to L.A.S.E.R. radiation.

2.5 Control Unit

As indicated earlier, the control unit 6 gives the possibility ofcontrolling the different elements making up the cutting-out apparatus,i.e. the femtosecond laser 1, the shaping system 3, the sweeping opticalscanner 4 and the optical focusing system 5.

The control unit 6 is connected to these different elements via one (orseveral) communication bus(es) giving the possibility:

-   -   of transmitting control signals such as        -   the phase mask to the shaping system,        -   the activation signal to the femtosecond laser,        -   the sweeping rate to the sweeping optical scanner,        -   the position of the sweeping optical scanner along the            displacement path,        -   the cutting-out depth to the optical focusing system.    -   receiving measurement data from the different elements of the        system such as        -   the sweeping rate attained by the optical scanner, or        -   the position of the optical focusing system, etc.

The control unit 6 may consists of one (or several) work station(s)and/or one (or several) computer(s) or may be of any other type known toone skilled in the art. The control unit 6 may for example comprise aportable telephone, an electronic tablet (such as an IPAD®), a personaldigital assistant (or “PDA”, an acronym of the expression “PersonalDigital Assistant”), etc. In every case, the control unit 6 comprises aprocessor programmed in order to allow control of the femtosecond laser1, of the shaping system 3, of the sweeping optical scanner 4, of theoptical focusing system 5, etc.

2.6 Pattern

The reconfigurable modulation of the wave front of the L.A.S.E.R. beamgives the possibility of generating multiple simultaneous impact points81 each having a size and a control position in the focusing plane 21.

These different impact points 81 form a pattern 8 in the focal plane 21of the modulated L.A.S.E.R. beam.

The number of impact points 81 of the pattern 8 decreases as many timesas the time required for the surgical cutting-out operation.

However, the size of the pattern 8, the number of impact points 81 whichit comprises and their respective positions relatively to thedisplacement direction are technical features cleverly selected formeeting technical constraints associated with the cutting-out of tissue,as this will emerge subsequently.

2.6.1. Constraints and Selected Solutions

2.6.1.1. Maximum Number of Impact Points Per Pattern

In order to accelerate the cutting-out of the tissue 2, it is preferableto have a pattern 8 including a maximum number of impact points 81. Inpresent ophthalmic laser systems, the energy per pulse and per spotrequired for corneal cutting-out is of the order of 1 μJ. Thus, with afemtosecond laser—such as a laser source Satsuma (marketed by AmplitudeSystéme)—providing a power of 20 W at a rate of 500 kHz, i.e. at most anenergy of 40 μJ/pulse, it is theoretically possible to generate apattern 8 consisting of 40 identical impact points 81.

However, in any laser system, losses occur along the optical trajectory.Thus, in a prototype tested by the Applicant, the power arriving on thecornea was only 12 W at most for a shaping of six impact points 81 of aglobal size (30 μm*22 μm). The diameter of the focus beam was a diameterof 8 μm, versus about 4 μm at most for present ophthalmic lasers. Withinthe scope of a prototype tested by the Applicant, a 4 times greaterenergy per spot was required as compared with present ophthalmic lasers,i.e. 4 μJ. Thus for this prototype, the use of a pattern consisting ofsix impact points 81 (at the most) was selected. Of course, if the powerof the femtosecond laser 1 is greater, the pattern 8 may comprise anumber of impact points 81 greater than six.

2.61.2. Distribution of the Impact Points in the Pattern

The six impact points 81 of the pattern 8 may be distributed accordingto different configurations.

For example the six impact points 81 may be distributed along a singleline. The total length of the pattern 8 is then equal to the sum betweenthe diameter of an impact point 81 and the center-to-center distancebetween the extreme impact points 81 of the pattern 8. The width of thepattern 8, as for it, is equal to the diameter of an impact point 81.

As indicated earlier, the shaping of the L.A.S.E.R. beam causes a powerloss, due to the energy dispersed over the optical path. The global sizeof the shaping (and therefore the size of the pattern 8) is part of thefactors having an influence on this energy loss.

The greater the size (in length or in width) of the pattern 8, thegreater is the power loss. A distribution of six impact points 81 on asingle line therefore induces a significant power loss.

As an indication:

-   -   a pattern 8 with a size of 30 μm*22 μm comprising six impact        points 81 causes a power loss of about 10%, while    -   a pattern 8 with a size of 84 μm*20 μm comprising five impact        points 81 causes a power loss of about 25%.

Thus, for a given number of impact points 81, “compacts” patterns (ratioof the sizes in length and in width close to 1) cause a lower energyloss.

This is why the impact points 81 of the pattern 8 are preferablycomprised in a surface for which the ratio between the length and thewidth is comprised between 1 and 4, preferentially between 1 and 2, andeven more preferentially between 1 and 1.5.

For example, the six impact points 81 a-81 f of the pattern nay bedistributed over first and second parallel lines 82, 83:

-   -   the first line 82 passing through three impact points 81 a-81 c        form a first triplet, and    -   the second line 83 passing through three other impact points 81        d-81 f forming a second triplet distinct from the first triplet.

A pattern corresponding to this distribution is illustrated in FIG. 5 .Advantageously, the impact points 81 a-81 f of the pattern may beshifted from one line to the other along the displacement direction D.More specifically, the impact points 81 a-81 c of the first triplet maybe shifted by a non-zero distance (along the displacement direction D)relatively to the impact points 81 d-81 f of the second triplet. Thisgives the possibility of avoiding superposition of cavitation bubbles inthe cutout plane during the displacement of the pattern 8 by thesweeping optical scanner 4.

2.6.1.3. Minimum Distance Between Impact Points of the Pattern

In addition to the distribution of the impact points 81 of the pattern8, another parameter of the pattern relates to the distance between theadjacent impact points.

This distance is defined by constraints related to the shaping system.

During the shaping operation of the L.A.S.E.R. beam stemming from thefemtosecond laser, “too close” impact points interfere with each otherbecause of the spatial coherence of the source. These interferencesdegrade the shape of the impact points and make it impossible to controlthe laser intensity level on each impact point. It is thereforepreferable that the distance between these adjacent impact points of thepattern be sufficient in order to limit this interference phenomenonbetween too close impact points.

This “sufficient distance” depends on the focusing of the beam. The morethe beam will be focused, the smaller will be this distance. Conversely,the less focused will be the beam, the larger will be this distance.

By taking into account the constraints of working distance related tothe surgical applications of the anterior segment of the eye, of thereproducibility of the shaping as well as of the aberrations of theoptical system degrading the spatial coherence of the beam, theseparation limit of two spots is located at about 10 μm.

This is why the “sufficient distance” from center-to-center between twoadjacent impact points is greater than 5 μm, preferentially greater than10 μm and even more preferentially comprised between 10 μm and 20 μm,notably between 10 μm and 15 μm.

2.6.1.4. Orientation of the Pattern Relatively to the DisplacementDirection

The basic form illustrated in FIG. 5 may be oriented in different waysin the lattice.

The most obvious orientation of this basic form for one skilled in theart is illustrated in FIG. 6 . This orientation consists of displacingthe pattern along a displacement direction D perpendicular to both lines82, 83 defined by the first and second triplets of impact points 81 a-81c and 81 d-81 f.

However, several limitations related to the shaping system and to thedisplacement direction of the pattern prevent the use of such anorientation.

As described earlier, the distance between two adjacent impact points 81a, 81 b of the pattern is preferentially greater than 10 μm. Bydisplacing the pattern along a displacement direction perpendicular toboth lines 82, 83 defined by the first and second triplets of impactpoints 81 a-81 c, 81 d-81 f, the distance between the cavitation bubblesgenerated on adjacent segments 42 a, 42 b, parallel to the displacementdirection of the pattern will be of the order of 15 μm.

Now, a “conventional” distance between adjacent cavitation bubbles forthe cutting-out of a cornea is of the order of 2 μm to 7 μm, notablyequal to 5 μm.

Therefore it is necessary to “tilt” the pattern 8 so that theneighboring cavitation bubbles generated on adjacent segments 42 a, 42 bparallel to the displacement direction D of the pattern 8 are spacedapart by a distance substantially equal to 5 μm in the displacementdirection.

It will be noted that on a same segment 42 a, the 5 μm distance betweentwo adjacent cavitation bubbles may be obtained by adjusting thedisplacement pitch of the sweeping optical scanner 4.

2.62. Examples Of Retained Patterns

With reference to FIGS. 7 to 9 , different examples of patterns whichmay be used with the cutting-out apparatus according to the inventionare illustrated.

In the embodiment illustrated in FIG. 7 , the pattern comprises threeimpact points 81 a-81 c extending along a line 82 of the pattern 8. Theimpact points are spaced apart by a distance “d” along the displacementdirection D. The line of the pattern is tilted by an angle “α”relatively to the displacement direction D of the sweeping opticalscanner 4 so that the cavitation bubbles along a straight lineperpendicular to the displacement direction D are spaced apart by adistance “e” in the cutout plane. One then has the followingrelationship between the different distances “d” and “e”,and the tiltangle “α”:

$\propto {= {\tan^{- 1}\left( \frac{e}{d} \right)}}$

Preferably, the tilt angle “α” of the pattern is comprised between 10°and 80°.

In the embodiment illustrated in FIG. 8 , the pattern comprises fourimpact points 81 a-81 d extending along two parallel lines 82, 83 of thepattern 8:

-   -   A first pair of impact points 81 a, 81 b extends along a first        line 82 of the pattern,    -   A second pair of impact points 81 c, 81 d extends along a second        line 83 of the pattern.

This pattern present has a square shape tilted with a tilt angle “a”relatively to the displacement direction of the sweeping opticalscanner. One has the following relationship:

$\propto {= {\tan^{- 1}\left( \frac{e}{d} \right)}}$

With:

-   -   “α” being the tilt angle of each line of the pattern relatively        to the displacement direction,    -   “d” corresponding to the distance between two adjacent impact        points, and    -   “e” corresponding to the distance between two adjacent impact        points along a direction perpendicular to the displacement        direction of the pattern.

In the embodiment illustrated in FIG. 9 , the pattern comprises siximpact points 81 a-81 f extending along two parallel lines of thepattern 8:

-   -   A first triplet of impact points extends along a first line of        the pattern,    -   A second triplet of impact points extends along a second line of        the pattern.

This pattern has a rectangular shape tilted with a tilt angle “a”relatively to the displacement direction of the sweeping opticalscanner. One has the following relationship:

$\propto {= {\tan^{- 1}\left( \frac{e}{d} \right)}}$

With:

-   -   “α” being the tilt angle of each line of the pattern relatively        to the displacement direction,    -   “d” corresponding to the distance between two adjacent impact        points, and “e” corresponding to the distance between two        adjacent impact points along a direction perpendicular to the        displacement direction of the pattern.

2.6.3. Theory Relative to the Determination of Patterns

In the following, an approach applied by the Applicant will be describedfor determining the possible shapes of the patterns of impact pointsgiving the possibility of finally obtaining an arrangement of cavitationbubbles consisting of a repetitive regular matrix:

-   -   either a square matrix,    -   or an equilateral triangle matrix,        while observing the minimum spacing between adjacent impact        points for limiting the interference phenomenon described        earlier.

There exists a variety of possible patterns for obtaining by projectionduring their displacement, a homogeneous and repetitive matrix ofcavitation bubbles distant from each other by 5 μm, over the wholetreated surface. But there also exists an “ideal” matrix, for which theimpact points are sufficiently far from each other for avoidinginterferences, and sufficiently close so that the total surface of thepattern is small and is included in a restricted field, which ispreferable because of the limited size of the optics and of the mirrorswhich are found on the path of the L.A.S.E.R. beam.

We simply proceeded with the observation of an arrangement of spots,either with a square matrix or with an equilateral triangle matrix, andwe determine the possible patterns for obtaining this arrangement, oncethe pattern is set into motion by the sweeping optical scanner.

2.6.3.1. Searching for a Pattern in Order to Obtain an Arrangement ofCavitation Bubbles as an Equilateral Triangle Matrix

In FIG. 10 illustrating a cut out plane including a plurality ofcavitation bubbles 100, an arrangement of bubbles as an equilateraltriangle forming a matrix 101 may be observed.

The observation, leads us to identify several possible patterns, whichare included in this matrix, as illustrated FIG. 11A, FIG. 11B, FIG.11C.

In practice, none of the three matrices shown above may be used. Indeed,if the distance separating 2 bubbles of the cut out surface is D, or 5μm, in order to avoid interferences the minimum distance between 2impact points of the pattern also has to be equal to 10 μm, i.e. atleast 2D.

Now, in the three examples of patterns illustrated in FIG. 11A, FIG.11B, FIG. 11C, there is always at least two impact points of the patterntoo close to each other (distance=D*(Cos(30°)*2)=1.73*D. I.e. for D=5μm, one has a distance of 8.65 μm (cf. FIG. 12 ).

These observations therefore lead us to define a pattern for which allthe impact points are at least distant from each other by 2*D and whichgives the possibility of obtaining the arrangement as an equilateraltriangle pattern.

A first pattern example is illustrated in FIGS. 13 to 15 , wherein allthe points are distant from each other at least by 2*D, i.e. for thedistances A and B if D=5 μm:

A=D*cos(30°)*4=17 μm

B=√{square root over ((2.5D)²+(cos(30°)*D)²)}=13.22 μm

On the other hand, the distance between the most spaced apart two pointsof the matrix is

C=√{square root over ((4.5D)²+(cos(30°)*5D)²)}=31.22 μm

Finally, in this matrix, accurate angulation (cf. FIG. 15 ) gives thepossibility of reproducing the regular pattern as an equilateraltriangle, and the angles relatively to the horizontal and to thevertical are:

A=D×cos(30°)×4

B=√{square root over ((2.5D)²+[(cos(30°)×D)]²)}

C=√{square root over ((4.5D)²+[(cos(30°)×5D)]²)}

α=19.1°

β=16.1°

A second example of a pattern is illustrated in FIGS. 16 to 18 , whereinall the points are distant from each other by at least 2*D, i.e. for thedistances A if D=5 μm:

A=√{square root over ((2.5D)²+(cos(30°)*D)²)}=13.22 μm

On the other hand, the distance between the two most spaced apart pointsof the matrix is

C=√{square root over ((5.5D)²+(cos(30°)*5D)²)}=35 μm

Finally, in this pattern, accurate angulation gives the possibility ofreproducing the equilateral triangle matrix, and the angles relativelyto the horizontal and to the vertical are:

A=√{square root over ((2.5D)²+[(cos(30°)×D)]²)}

C=√{square root over ((5.5D)²+[(cos(30°)×5D)]²)}

α=19.1°

β=16.1°

From the foregoing, we have just demonstrated that two differentpatterns may be used for obtaining after setting into motion, anarrangement of regular bubbles positioned according to a matrix as anequilateral triangle.

The selection between the first or the second pattern would rather be infavor of the first, since the maximum spacing between the most distant 2points is 31.22 μm instead of 35 μm, therefore a more compact shape.

Another benefit of these patterns, is that the number of points may beincreased to more than 6 (2×3 points) by adding new rows of points, byobserving the same distances and angulations and by passing to patternsof 9 (3×3) or 12 points (3×4) or more.

2.6.3.2. Searching for a Pattern in Order to Obtain a Cavitation BubbleArrangement as a Square Matrix

In FIG. 19 , illustrating a cut out plane including a plurality ofcavitation bubbles 100, a square arrangement of bubbles forming a matrix101 may be observed.

The observation leads up to identifying a possible pattern, which isincluded in this matrix, and which observes the minimum spacing between2 points equal to twice the distance D:

A=√{square root over (8D ²)}=14.14 μm

B=√{square root over (5D ²)}=11.18 μm

E=3D=15 μm.

On the other hand, the distance between the two most spaced apart pointsof the pattern is:

C=√{square root over (41D ²)}=32 μm

Finally, in this matrix, accurate angulation gives the possibility ofreproducing the regular pattern as a square, and the angle relatively tothe horizontal is α=26.56.

2.6.3.3. Particular Case of Interlaced Patterns

We have described the principle of the use of patterns of laser spotsfor obtaining a homogeneous arrangement of cavitation bubbles in thetreated tissue. These patterns have a particular arrangement of laserspots, including the positioning relatively to each other, and thedistances which separate them, give the possibility of observing theconstraints discussed above, and notably the minimum distance betweeneach spot in order to avoid interferences, and the maximum distancebetween each impact point in order to obtain a satisfactory cut outquality of the tissue. The patterns shown up to now, all have theparticularity of giving the possibility when a movement is applied tothem by the printed sweeping by the scanner, of uniformly and regularlycovering a surface of equidistant cavitation bubbles, without leavinguntreated areas. At the end of a segment having a regular arrangement ofimpact points, as indicated in FIG. 23 , the scanner controls thedisplacement of the matrix by a pitch 106 equal to the distance betweenthe rows of the most far away impacts 104, increased by the distancebetween two contiguous lines 105.

An alternative pattern shown in FIG. 24 , gives the possibility ofimagining the leaving of an untreated area ZNT as shown in FIG. 25 ,this ZNT area may be treated with the next sweep with an arrangement ofinterlaced impact points. For this, the pitch printed by the scannerbetween two successive segments is not constant and will be for once outof two occurrences equal to twice the distance between two contiguousrows of impacts 107, and once out of two equal to the distance betweenthe farthest impact rows 108, increased by the distance between twocontiguous lines 105.

2.63.4 Particular Case of a Pattern with a Central Impact Point

With reference to FIG. 28 , another pattern example is illustrated whichmay be used for cutting-out a tissue. This pattern comprises a plurality(i.e. at least three) of peripheral impact points 81P, and a centralimpact point 81B positioned at the center of gravity of the pattern,notably in the example illustrated in FIG. 28 , at the intersectionbetween diagonal axes passing through opposite peripheral impact points.

The presence of this central impact point gives the possibility ofmaking use of the phenomena generating an energy in the center of thepattern (a phenomenon known under the name of “zero order”). Indeed,during the phase modulation of the L.A.S.E.R. beam 11 with the shapingsystem 3, a portion of the L.A.S.E.R. beam, stemming from thefemtosecond laser is not modulated (because of the existing spacebetween the pixels of the liquid crystals of the SLM). This portion ofthe non-modulated L.A.S.E.R. beam may induce the generation of an energypeak being formed at the center of the SLM.

When the pattern does not comprise any impact point at this center ofgravity, it is necessary to limit this energy peak of zero order inorder to avoid untimely generation of cavitation bubbles during thedisplacement of the pattern in the cutout plane.

2.6.3.5 Remarks

We have described how to position the impact points of a multipointlaser beam, so that the generated bubbles have a homogeneous and regulararrangement on the cutting-out surface of the tissue. From among aninfinity of non-regular arrangements, which may also be used, we havedemonstrated that in order to obtain a regular arrangement as anequilateral triangle, there existed two types of preferred patterns andthat in order to obtain a regular square arrangement, there existed apreferred pattern. For all the preferred matrices, the spacings andangles between each point of the matrix were calculated.

Of course, the invention also deals with any type of pattern for whichthe impact points are sufficiently spaced apart from each other in orderto avoid interferences and the movement of which gives the possibilityof obtaining by projection a relatively homogenous cover of the surfaceto be cut out, even without regular repetition of a geometrical matrix,even if the shown matrices give better results.

The drawback of this type of pattern shapes is the introduction of an“initiation area” 102 at the periphery of a regular area 103. In thisinitiation area 102, the cutting-out is incomplete, as illustrated inFIG. 22 . Although the size of this initiation area 102 is very smallwith respect to the global size of the cut out (less than 0.5% of a 8 mmcorneal cap diameter for the shown examples), this initiation area 102will preferably have to be as short as possible.

2.6.4 Cutting-Out Device Relative to the Pattern and Associated Process

In summarizing the preceding paragraphs concerning the differentcharacteristics relative to the pattern, the inventors have proposed anapparatus for cutting out human or animal tissue, such as a cornea, or acrystalline, the apparatus including a femtosecond laser capable ofsending a L.A.S.E.R. beam in the form of pulses, and a treatment devicearranged downstream of the femtosecond laser for processing theL.A.S.E.R. beam generated by the femtosecond laser, the treatment devicecomprising:

-   -   a shaping system 3 positioned on the trajectory of said beam to        modulate the phase of the wave front of the L.A.S.E.R. beam so        as to obtain a phase-modulated L.A.S.E.R. beam according to a        modulation set value calculated to distribute the energy of the        L.A.S.E.R. beam into at least two impact points 81 forming a        pattern 8 in its focal plane 21 corresponding to a cutout plane,        each impact point producing a cut-out,    -   a sweeping optical scanner 4 arranged downstream of the shaping        system for shifting the pattern in the cutout plane into a        plurality of positions 43 according to a direction of        displacement D,    -   a control unit including a processor programmed to allow control        of the femtosecond laser, the shaping system and the sweeping        optical scanner to incline the pattern relative to the direction        of displacement such that at least two impact points of the        pattern are spaced apart from:    -   a non-zero distance according to a first axis parallel to the        direction of displacement on the one hand, and    -   a non-zero distance according to a second axis perpendicular to        the direction of displacement on the other hand.

Advantageously, the pattern can comprise at least two (especially three)adjacent impact points extending along a line of the pattern, the anglebetween said line of the pattern and the direction of displacement beingbetween 10 and 80°, preferably between 15° and 40°, and even morepreferably between 19° and 30°. Also, the pattern can comprise:

-   -   a first set of at least two (especially three) impact points        arranged along a first line of the pattern, and    -   a second set of at least two (especially three) other impact        points arranged along a second line of the pattern parallel to        the first line.

The pattern can also comprise at least one other set of impact pointsarranged along at least one other line of the pattern, parallel to thefirst and second lines. The impact points of the second set can beoffset by a non-zero distance relative to the impact points of the firstset. As a variant, each impact point of the second set can be alignedwith a respective impact point of the first set according to a straightline perpendicular to the direction of displacement. Advantageously, thedistance between two adjacent impact points of the pattern can begreater than 5 μm, preferably greater than 10 μm and even morepreferably between 10 and 15 μm. The pattern can also be registered in asurface whereof the ratio between the length and the width is between 1and 4, preferably between 1 and 2, and even more preferably between 1and 1.5. Finally, the pattern can comprise a central impact pointpositioned at the barycenter of the pattern.

The inventors have also proposed a process for controlling a cutting-outapparatus including a femtosecond laser capable of sending a L.A.S.E.R.beam in the form of pulses, and a treatment device arranged downstreamof the femtosecond laser for processing the L.A.S.E.R. beam, thetreatment device comprising a shaping system and a sweeping opticalscanner, the process comprising the steps consisting of:

-   -   modulating, by using the shaping system, the phase of the wave        front of the L.A.S.E.R. beam so as to obtain a phase-modulated        L.A.S.E.R. beam according to a modulation set value calculated        to distribute the energy of the L.A.S.E.R. beam into at least        two impact points 81 forming a pattern in its focal plane        corresponding to a cutout plane, each impact point producing a        cut-out,    -   displacing, by using the sweeping optical scanner, the pattern        in the cutout plane into a plurality of positions according to a        direction of displacement D,    -   inclining the pattern relative to the direction of displacement        such that at least two impact points of the pattern are spaced        apart from:    -   a non-zero distance according to a first axis parallel to the        direction of displacement on the one hand, and    -   a non-zero distance according to a second axis perpendicular to        the direction of displacement on the other hand.

Advantageously, the step consisting of modulating can comprise theformation of a pattern comprising at least two (especially three)adjacent impact points extending along a line of the pattern, the anglebetween said line of the pattern and the direction of displacement beingbetween 10 and 80°, preferably between 15° and 40°, and even morepreferably between 19° and 30°. Also, the step consisting of modulatingcan comprise the formation of a pattern having:

-   -   a first set of at least two (especially three) impact points        arranged along a first line of the pattern, and    -   a second set of at least two (especially three) other impact        points arranged along a second line of the pattern parallel to        the first line.

The step consisting of modulating can also comprise the formation of apattern having at least one other set of impact points arranged along atleast one other line of the pattern, parallel to the first and secondlines. The step consisting of modulating can also comprise the formationof a pattern wherein the impact points of the second set are offset by anon-zero distance relative to the impact points of the first set. As avariant, the step consisting of modulating can comprise the formation ofa pattern wherein each impact point of the second set is aligned with arespective impact point of the first set according to a straight lineperpendicular to the direction of displacement.

Advantageously, the step consisting of modulating can comprise theformation of a pattern wherein the distance between two adjacent impactpoints is greater than 5 μm, preferably greater than 10 μm and even morepreferably between 10 and 15 μm.

The step consisting of modulating can also comprise the formation of apattern registered in a surface whereof the ratio between the length andthe width is between 1 and 4, preferably between 1 and 2, and even morepreferably between 1 and 1.5. Finally, the step consisting of modulatingcan also comprise the formation of a pattern having a central impactpoint positioned at the barycenter of the pattern.

3. OPERATING PRINCIPLE

The principle of the operation of the cutting-out apparatus illustratedin FIG. 1 will now be described with reference to the destruction of alens within the scope of an operation of the cataract. It is quiteobvious that the present invention is not limited to the operation of acataract.

In a first step, the control unit 6:

-   -   transmits to the shaping system 3 a first phase mask associated        with a first treatment pattern    -   emits a control signal to the optical focusing system 5 for        displacing the focusing plane at a first deep cutout plane in        the eye,    -   activates the displacement of the sweeping optical scanner 4 as        far as an initial cutting-out position. The sweeping being        accomplished in X, Y, the scanner is equipped with a mirror, X,        which allows sweeping along each segment of the displacement        path of the pattern, and another mirror Y, which allows, once a        segment has been completed, the changing of segment. The mirrors        X and Y therefore operate alternately with each other.

When the focusing system 5 and the optical scanner 4 are in position andthat the phase mask is loaded into the shaping system 3, the controlunit 6 activates the femtosecond laser 1. The latter generates aL.A.S.E.R. beam 11 which crosses the shaping system 3. The shapingsystem 3 modulates the phase of the L.A.S.E.R. beam. The phase-modulatedL.A.S.E.R. beam 31 leaves the shaping system 3 and enters the opticalscanner 4 which deviates the modulated L.A.S.E.R. beam 31. The modulatedand deviated LA.S.E.R. beam 41 enters the optical focusing system 5which focuses the beam in the first cutout plane.

Each impact point 81 of the pattern 8 produces a cavitation bubble. Thefemtosecond laser 1 continues to emit other pulses as a LA.S.E.R. beamat a determined rate. Between each pulse, the mirror X has pivoted by acertain angle, which has the consequence of displacing the pattern 8 andof producing new cavitation bubbles shifted relatively to the previousones, until a line is formed. Thus, a first plurality of cavitationbubbles forming a line is formed in the cutout plane, these bubblesbeing laid out according to the cutting-out pattern 8. By having thedisplacement speed of the mirror and/or the generation rate of pulsesvaried by the femtosecond laser, it is possible to have the distancebetween two successive patterns varied.

Once this plurality of bubbles forms a complete line, the control unit 6disables the L.A.S.E.R. source 1, controls the stopping of the pivotingof the mirror X and controls the pivoting of the mirror Y of the opticalscanner 4 as far as the next cutting-out position depending on thesweeping pitch of the optical scanner 4, and then again controls therestarting of the pivoting of the mirror X in the opposite direction.When the optical scanner 4 is in position and the mirror X has attainedits constant set speed value, the control unit 6 again activates thefemtosecond laser 1. The L.A.S.E.R. beam 11 crosses the shaping system3, the optical scanner 4 and the optical focusing system 5. A secondsequence of a plurality of cavitation bubbles is formed in the firstcutout plane forming a new line parallel to the previous one andjuxtaposed.

These operations are repeated in the whole first cutout plane.

When the optical scanner 4 has swept all the surface of the first cutoutplane, a first cutting-out area (the shape and the dimensions of whichare controlled by the control unit 6) is generated.

The control unit 6 disables the femtosecond laser 1 and controls:

-   -   the translational displacement of the lens(es) of the optical        focusing system 5 for displacing the focusing plane 21 in a        second cutout plane,    -   the rotary displacement of the mirror(s) of the optical scanner        4 towards an initial cutting-out position of the second cutout        plane,    -   the optional loading by the shaping system 3 of another phase        mask for modifying the positioning and/or the size of the impact        points of the pattern, etc.

The control unit 6 repeats the operations for controlling thefemtosecond laser 1, the shaping system 3, the sweeping optical scanner4 and the focusing system 5 in the second cutout plane, and moregenerally in the successive cutout planes.

At the end of these different steps, a stack of cutout planes isobtained corresponding to the volume to be destroyed 23.

4. CONCLUSIONS

Thus, the invention gives the possibility of having an efficientcutting-out tool. The dimensions of the impact points of the patternbeing substantially equal (the shape, position and diameter of each spotare dynamically controlled by the calculated phase mask and displayed onthe SLM and which may correct the irregularities), the cavitationbubbles which pull to pieces the cut out biological tissues will be ofsubstantially equal sizes. This gives the possibility of improving thequality of the obtained result, with a homogeneous cutout plane, inwhich the residual tissue bridges all has substantially the same sizeand which allows dissection by the practitioner of acceptable qualityconsidering the importance of the quality of the surface condition ofthe cut out tissue when for example this is a cornea.

The invention was described for operations for cutting-out a cornea inthe field of ophthalmological surgery, but it is obvious that it may beused for another type of operation in ophthalmological surgery withoutdeparting from the scope of the invention. For example, the inventionfinds application in corneal refractive surgery, such as the treatmentof ametropias, notably nearsightedness, farsightedness, astigmatism, inthe treatment of loss of accommodation, notably farsightedness.

The invention also finds application in the treatment of cataract withincision of the cornea, cutting-out of the anterior of the lens, andfragmentation of the lens. Finally, in a more general way, the inventionrelates to all clinical or experimental applications on the cornea orthe lens of a human or animal eye.

Still more generally, the invention relates to the vast field ofL.A.S.E.R. surgery, and finds an advantageous application when thepurpose is to cut out and more particularly vaporize human or animalsoft tissues, with a high water content.

The reader will have understood that many modifications may be made tothe invention described earlier without materially departing from thenovel teachings and advantages described here.

For example, in the different embodiments described earlier, the opticalfocusing system positioned downstream from the sweeping optical scannerwas described as comprising a single module giving the possibility:

-   -   of focusing the modulated and deviated L.A.S.E.R. beam on the        one hand, and    -   of displacing the focusing plane in different cutout planes on        the other hand.

Alternatively, the optical focusing system may consist of two distinctmodules each ensuring one of these functions:

-   -   a first module—a so-called “depth positioning module”—positioned        upstream from the sweeping optical scanner and allowing        displacement of the focusing plane in different cutout planes.    -   a second module—a so called “concentrator module” positioned        downstream from the sweeping optical scanner and allowing        focusing of the modulated and deviated L.A.S.E.R. beam.

Likewise in the different embodiments described earlier, the shapingsystem described was an SLM. As a variant, the shaping system could becomposed of a plurality of phase masks, each phase mask acting on thephase of the L.A.S.E.R. beam to distribute the energy of the L.A.S.E.R.beam by phase modulation according to a pattern distinct. Each phasemask can for example be constituted by a plate (transparent to theL.A.S.E.R. beam) of variable thickness obtained by etching.

In this case, the phase masks can be fixed to a displacement device forshifting each phase mask between:

-   -   an active position in which the phase mask cuts the optical path        of the L.A.S.E.R. beam,    -   an inactive position in which the phase mask does not extend        over the optical path of the L.A.S.E.R. beam

The displacement device is for example constituted by a mobile supportin rotation around an axis of rotation parallel to the optical path ofthe L.A.S.E.R. beam, the mobile support being arranged so as to enablethe positioning of a respective phase mask on the optical path of theL.A.S.E.R. beam so as to modulate the phase of the latter. But thissolution needs mechanical elements to be introduced to the apparatus(displacement device) and therefore does not constitute a preferredsolution.

Also, in the description above, the control unit sent a control signalto the shaping system (such as a phase mask in the event where theshaping system is a spatial light modulator) for distributing the energyof the L.A.S.E.R. beam (via phase modulation) into at least two impactpoints forming a pattern in its focal plane. As a variant, the controlunit can be programmed to send several separate control signals forgenerating patterns different to each other. This modifies the intensityprofile of the L.A.S.E.R. beam according to different patterns in theplane of the cut-out, for example to improve the quality of the cut-outin the region of the contours of the cut-out surface in the cutoutplane.

Therefore, all the modifications of this type are intended to beincorporated within the scope of the appended claims.

1. An apparatus configured to cut a human or animal tissue, saidapparatus including a femtosecond laser capable of emitting a laser beamin the form of pulses and a treatment device for treating the laser beamgenerated by the femtosecond laser, the treatment device beingpositioned downstream from said femtosecond laser, wherein the treatmentdevice comprises: a shaping system positioned on the trajectory of saidbeam, the shaping system including a spatial light modulator programmedusing at least one phase mask to modulate the phase of the wavefront ofthe laser beam so as to obtain a modulated laser beam, a sweepingoptical scanner downstream from the shaping system, an optical focusingsystem downstream from the sweeping optical scanner, the opticalfocusing system comprising a concentrator module for focusing thephase-modulated laser beam in a focal plane and a depth-positioningmodule for displacing the focal plane into a plurality of cuttingplanes.
 2. The apparatus according to claim 1, wherein the modulatedlaser beam focuses onto at least two impact points forming a pattern inthe focal plane, and wherein the treatment device further comprises acontrol unit of the sweeping optical scanner configured to control thedisplacement of the pattern along a displacement path comprising atleast one segment in the focal plane.
 3. The apparatus according toclaim 2, wherein the control unit is configured to control theactivation of the femtosecond laser such that a distance between twoadjacent positions of the pattern along a segment of the displacementpath is greater than or equal to the diameter of an impact point of thepattern.
 4. The apparatus according to claim 2, wherein the control unitis configured to control the displacement of the pattern along adisplacement path comprising a plurality of segments, the distancebetween two adjacent segments of the displacement path being greaterthan the dimension of the pattern along an axis perpendicular to theplurality of segments.
 5. The apparatus according to claim 2, whereinthe control unit is configured to control the displacement of thepattern along a displacement path comprising a plurality of parallelsegments, the distance between two neighboring segments of thedisplacement path being constant and less than or equal to 3N times thediameter of an impact point, where N corresponds to the number of impactpoints of the pattern.
 6. The apparatus according to claim 2, whereinthe control unit is configured to control the displacement of thepattern along a displacement path comprising a plurality of parallelsegments, the distance between at least two neighboring segments beingdifferent from the distance between at least two other neighboringsegments.
 7. The apparatus according to claim 2, wherein the controlunit is configured to control the displacement of the pattern along anotch-shaped displacement path in the focal plane.
 8. The apparatusaccording to claim 2, wherein the control unit is configured to controlthe displacement of the pattern along a spiral-shaped displacement pathin the focal plane.
 9. The apparatus according to claim 2, wherein thesweeping optical scanner includes at least one optical mirror pivotingaround at least two axes, and wherein the control unit is configured tocontrol the pivoting of the mirror so as to displace the pattern alongthe displacement path.
 10. The apparatus according to claim 1, whichfurther comprises at least one Dove prism positioned between the shapingsystem and the sweeping optical scanner.
 11. The apparatus according toclaim 2, wherein the control unit is configured to control theactivation of the femtosecond laser, wherein the control unit activatesthe femtosecond laser when a sweeping rate of the sweeping opticalscanner is greater than a threshold value.
 12. The apparatus accordingto claim 1, which also comprises a filter arranged downstream from theshaping system to block parasite energy generated at the center of theshaping system.
 13. The apparatus according to claim 12, wherein thefilter comprises a plate including: an opaque zone which blocks laserradiation, wherein said opaque zone is arranged at the center of theplate, and a transparent zone which does not block laser radiationwherein said transparent zone is located at the periphery of the opaquezone. 14-16. (canceled)
 17. The apparatus according to claim 1, whereinthe at least one phase mask is calculated using an iterative algorithmbased on the Fourier transform.
 18. The apparatus according to claim 1,wherein each phase mask is a two-dimensional image, each point of whichis associated with a respective pixel of the spatial light modulator,wherein said two-dimensional image determines the final energydistribution of the modulated laser beam in the focal plane.
 19. Theapparatus according to claim 1, wherein said at least one phase mask iscalculated to obtain a single modulated laser beam, and to distributethe energy of the single modulated laser beam onto at least two impactpoints within the focal plane.
 20. The apparatus according to claim 1,wherein said at least one phase mask is calculated to modify thegeometric shape of an impact point of the modulated laser beam in thefocal plane.